How Your Building’s Fire Detection System Works: Panels, Circuits and Interfaces

Estimated reading time: 11 minutes

When most people think about a fire detection system, they think about smoke detectors and warning alarms.

Smoke detectors and warning devices are often the most visible parts of the system. However, the Fire Indicator Panel may also receive information from other fire safety equipment and send signals that cause doors, lifts, ventilation systems, warning systems and other building services to respond.

Understanding a few basic terms — particularly inputs, outputs, circuits and interfaces — makes it much easier to understand what the panel is doing and why two apparently similar buildings can have very different fire detection system arrangements.

Key Takeaways

✔ The Fire Indicator Panel is the central control point that receives inputs, displays system conditions and initiates required outputs.

✔ The interfaces and functions provided are determined by the requirements and approved design for the particular building, so two buildings can operate very differently.

✔ Interfaces can bring signals into the Fire Indicator Panel, send signals out to other systems, or do both.

✔ Not every detection input necessarily produces the same response. Some inputs may operate building services without immediately activating every warning or external alarm function.

✔ A Cause and Effect Matrix is a simple way of showing which outputs are intended to occur in response to different inputs or conditions.

✔ Where a building is externally monitored for brigade response, Alarm Signalling Equipment helps transmit monitored alarm signals through an approved service provider to Fire and Rescue NSW.

The Terminology at a Glance

Term	In simple terms
Fire Indicator Panel (FIP)	The central control and indicating point for the fire detection system.
Circuit	A wiring or communication path connecting devices or equipment with the FIP. Conventional detection circuits and addressable loops are different types of circuit arrangement.
Conventional detection circuit	A type of circuit that commonly leaves the FIP, passes through a group of devices and terminates at an end-of-line (EOL) device.
End-of-line (EOL) device	A device fitted at the end of a supervised circuit so the FIP or other control equipment can monitor the circuit wiring for certain fault conditions.
Addressable loop	A type of circuit that leaves the FIP, passes through addressable devices and returns to the panel.
Zone	An area or programmed group used to indicate where an alarm or event has occurred. A zone is not necessarily the same thing as a circuit.
Interface	The connection through which the fire detection system exchanges signals with another system. An interface can provide an input to the FIP, an output from the FIP, or both.
Input	A signal or condition received by the FIP — for example a detector activation, sprinkler flow switch or equipment fault.
Output	A signal or action initiated by the fire detection system — for example occupant warning, lift recall or air-conditioning shutdown. Control outputs may be provided through relays or interface modules.
Relay / relay output	An electrical switching contact used by the FIP or an interface module to provide a control signal to other equipment.
Trip	The control function or signal that causes another item of equipment to operate or change state, such as a mechanical shutdown. A relay is one common way of providing a trip.
Alarm Signalling Equipment (ASE)	Equipment used to transmit monitored alarm or other configured signals from the building to an external fire alarm monitoring service.
Cause and Effect	A simple way of documenting which outputs or functions are intended to occur in response to particular inputs or conditions.

What Is the Fire Indicator Panel?

The Fire Indicator Panel (FIP) is the main control and indicating point for the building’s fire detection system.

It receives information from devices and other equipment throughout the building and displays conditions such as alarms, faults and isolations. It can also initiate outputs that make other equipment respond.

Depending on the building, inputs to the FIP may include:

·  Smoke detectors

·  Heat detectors

·  Manual call points

·  Sprinkler flow or pressure switches

·  Fire pump or valve status signals

·  Fault signals from interfaced equipment

Outputs from the FIP may include:

·  Activating occupant warning equipment

·  Releasing smoke or fire doors

·  Recalling lifts

·  Shutting down air-conditioning equipment

·  Operating or interfacing with smoke-control systems

·  Releasing access-controlled doors

·  Transmitting an alarm through Alarm Signalling Equipment

In a simple building, the panel may perform only a small number of these functions. In another building, the FIP may sit at the centre of a much broader fire safety response involving several different systems.

What Determines What the Panel Is Supposed to Do?

The functions of a Fire Indicator Panel are not simply chosen by the panel manufacturer or fire contractor. They arise from the requirements and approved design for the particular building.

Depending on the building and when it was designed or modified, those requirements may be reflected in the applicable Building Code of Australia / National Construction Code provisions, referenced standards such as the applicable edition of AS 1670.1, approved drawings and specifications, and any fire engineering or Performance Solution documentation that applies to the building.

That is why two buildings with similar-looking panels can have very different interfaces and responses. One may only need detection and occupant warning. Another may also need lift recall, smoke-door release, mechanical shutdown, smoke-control interfaces and automatic fire alarm monitoring.

For an existing building, the important question is not simply what a current standard says in isolation, but what the building was approved and required to do, including any later approved changes. We deal with that regulatory pathway in more detail elsewhere in this series.

Inputs and Outputs: Information In, Instructions Out

One useful way to understand the system is to think in terms of inputs and outputs.

An input is information received by the Fire Indicator Panel. It tells the panel that something has happened or that another system is in a particular condition.

·  A smoke detector detects smoke

·  A manual call point is activated

·  A sprinkler flow switch operates

·  A fire pump reports a fault

·  A valve or other monitored item changes state

An output is a signal or action initiated by the fire detection system in response to an input or condition.

·  Warning speakers or sounders activate

·  A smoke door is released

·  A lift is recalled

·  Air-conditioning equipment is shut down

·  A monitored alarm signal is transmitted externally

The important point is that not every input produces every output. The required response depends on the purpose of that input and the approved design of the building.

Circuits: The Paths That Connect the System

A circuit is the wiring or communication path that connects devices or equipment with the Fire Indicator Panel. Different fire detection systems use different circuit arrangements.

The panel also supervises relevant circuits so it can recognise the conditions it is designed to monitor, including certain wiring or communication faults. On many conventional circuits, an end-of-line (EOL) device forms part of this supervision arrangement. This is different from external alarm monitoring, which involves information being transmitted outside the building.

An EOL device is fitted at the end of a supervised circuit so the panel can recognise the normal condition of the circuit and identify certain wiring faults. It is not an alarm input in its own right; it forms part of the circuit supervision arrangement.

Conventional Detection Circuits

A conventional detection circuit commonly leaves the Fire Indicator Panel, passes through a group of detectors or other devices and terminates at an end-of-line (EOL) device. The panel generally identifies the circuit or associated alarm zone rather than the individual conventional detector involved.

Addressable Loops

An addressable loop is another type of circuit arrangement. The cable leaves the Fire Indicator Panel, passes through individually addressed devices and returns to the panel. The panel can therefore communicate with individual addressable devices on the loop.

Article 3 looks at the practical differences between conventional and addressable systems in more detail, including fault finding, wiring resilience, replacement and future expansion.

What Is a Zone?

A zone is the area or programmed group used by the fire detection system to indicate where an alarm or other event has occurred. For example, a building might have zones identified as Basement, Ground Floor, Level 1 and Level 2.

A zone is therefore mainly about location and indication. A circuit describes how equipment is physically or electronically connected. In some conventional systems a detection circuit may correspond closely with an alarm zone, but the two terms do not mean the same thing.

What Is an Interface?

An interface is the point where the fire detection system exchanges a signal with another piece of equipment or another building system.

Using the input/output language we’ve described, an interface can provide an input to the Fire Indicator Panel, an output from the panel, or both. The direction matters because the panel may be receiving information from another system, telling another system to do something, or exchanging information in both directions.

Relays and Trips: Terminology You May Hear

A common way for the fire detection system to provide a hard-wired output to another piece of equipment is through a relay. A relay provides electrical contacts that change state when the required fire-system condition occurs.

Fire contractors will often refer to the control function produced by that output as a trip. For example, the FIP may provide a mechanical shutdown trip, lift recall trip or door-release trip. The distinction is useful: the relay is the switching device or contact; the trip is the function being initiated.

In a conventional arrangement, the relay may be located at the FIP or associated interface hardware. In an addressable system, an addressable output module on the detection loop can provide a relay contact closer to the equipment being controlled. A simple relay contact is therefore different from an EOL device: the relay provides a control output, while the EOL forms part of supervision of a monitored circuit. The exact wiring and supervision requirements depend on the equipment and the approved system design.

Common Output Interfaces

System	Typical output from the fire detection system
Fire or smoke doors	The FIP may release magnetic door holders so doors close.
Lifts	The FIP may provide a trip signal for lift recall or another required fire-mode response.
Air-conditioning / mechanical services	The FIP may provide a shutdown trip to air-handling equipment or initiate another smoke-control response.
Occupant warning systems	The FIP may activate sounders, speakers, tones or recorded messages.
Security / access control	The FIP may release electronically locked doors or signal an access-control system to support evacuation.

Common Input Interfaces

System	Typical input to the Fire Indicator Panel
Sprinkler system	A flow or pressure switch may signal that the sprinkler system has operated.
Fire pumps	The FIP may receive pump-running, fault or power-supply status signals.
Valves / monitored equipment	The FIP may receive a change-of-state or fault signal.
Other fire or building systems	The FIP may receive alarm, fault or status information through an interface.

Some interfaces can involve signals in both directions. The important question is what information is meant to pass through the interface and what response is required when it does.

Does Every Detection Input Cause the Same Alarm Response?

No. A device can be part of the building’s fire detection arrangements without every activation producing exactly the same warning, monitoring or building-control response.

For example, smoke detection can be provided specifically to initiate automatic shutdown of air-handling equipment. The NCC recognises that smoke detectors provided solely for that shutdown function need not necessarily activate the building occupant warning system. In that type of arrangement, the purpose of the detector is to stop the mechanical system from continuing to move air and potentially distribute smoke through the building.

Other systems may incorporate an alarm acknowledgement or investigation facility where the applicable requirements allow it. Such arrangements can provide a defined opportunity for an alarm condition to be acknowledged and investigated before the system progresses to its full programmed response. That does not mean an alarm can simply be cancelled at will; the facility and timing must be part of the approved system design.

This is one reason the question “what happens when this detector activates?” can be more useful than simply asking whether the building has smoke detection.

What Is a Cause-and-Effect Matrix?

Whenever an input is intended to produce a particular response, there is a cause-and-effect relationship. A Cause-and-Effect Matrix is a simple visual way of documenting those relationships.

In plain English: the cause is the input or condition; the effect is what the system is intended to do as a result.

A simplified example might look like this:

Cause / input	FIP indication	Occupant warning	Mechanical shutdown	Lift recall	External monitoring / ASE
Common-area smoke detector	✓	✓	✓	✓	✓
Duct detector for AHU shutdown	✓	—	✓*	—	—
Manual call point	✓	✓	✓	✓	✓
Sprinkler flow switch	✓	✓	✓	✓	✓
FIP power-supply fault	Fault	—	—	—	Fault signal

* After the detector has been in a non-alarm state of not less than 60 seconds and not more than 90 seconds the fire panel shall initiate a control signal to restart the supply fan.

NOTE THE ABOVE IS AN ILLUSTRATIVE EXAMPLE ONLY.

Actual responses depend on the requirements and approved design of the particular building.

Real Cause and Effect Matrices can contain many more inputs and outputs. The value of the matrix is that it gives contractors, building managers and designers a clear reference for what should happen when different events occur.

What Does External Fire Alarm Monitoring Look Like?

External monitoring is different from the Fire Indicator Panel supervising its own circuits. External monitoring means that selected alarm information is transmitted outside the building to a monitoring service.

In NSW, an Automatic Fire Alarm system that is connected for Fire and Rescue NSW response is monitored through an approved Automatic Fire Alarm Service Provider (AFASP). The building’s Alarm Signalling Equipment (ASE) provides the communications link from the fire detection system to that external service.

The ASE is usually a separate piece of equipment installed at, near or associated with the Fire Indicator Panel. Its exact appearance varies by provider and installation, but it is not simply another smoke detector and it is not the Fire Indicator Panel itself.

This is an example of a Romteck Grid ASE. Actual hardware and indicators vary by provider and installation.

For an alarm signal that is configured for brigade monitoring, the simplified path is:

The approved monitoring provider sits between the building’s ASE and FRNSW dispatch. Fire and Rescue NSW receives automatic fire alarm calls at its Communication Centres. When a monitored fire alarm is received through the approved service arrangements, FRNSW dispatch processes the incident and the appropriate fire brigade resources are responded to the building.

This distinction is important because the monitoring centre or AFASP is not itself the fire brigade. It is the approved service that receives and passes the monitored alarm information into the FRNSW response system.

Not every building is externally monitored, and not every signal generated by a Fire Indicator Panel necessarily results in a fire brigade response. Alarm, fault and other monitored conditions can have different transmission and response arrangements depending on how the building has been configured and what monitoring is required.

Why Understanding These Connections Matters

As we’ve covered, a fire detection system may receive information from, and send signals to, a range of other fire safety and building systems.

Those connections become important whenever the system is tested, altered, upgraded or replaced. A change to one part of the system may affect interfaces or functions elsewhere, even where the equipment being changed appears relatively simple.

It is also why two buildings with apparently similar Fire Indicator Panels can operate quite differently. The functions provided in each building depend on the applicable requirements and the building’s approved design.

Understanding an existing system is much easier where accurate drawings, Cause and Effect information and other relevant building documentation are available. Where documentation is incomplete, additional investigation may be required to establish how the system is intended to operate.

Final Thoughts

A fire detection system is much more than a collection of smoke detectors.

The Fire Indicator Panel receives inputs, displays system conditions, supervises parts of the installation and initiates outputs through interfaces with other building services. The exact functions and responses depend on the requirements and approved design of the particular building.

Understanding interfaces, inputs, outputs, circuits, circuit supervision, relay and trip terminology, Cause and Effect and external monitoring provides the foundation for the more detailed decisions that come later.

In the next article, we look specifically at one of those decisions: the difference between conventional and addressable fire detection systems and what that difference means for strata buildings.

Want us to cover another topic?

Some of the concepts discussed in this article are explored in more detail elsewhere in our fire detection and alarm systems article library, and we’ll continue adding new topics over time. If there’s a fire safety question or topic you’d like us to explain, send your suggestion to info@fcfire.com.au.

About the Author

This article was prepared by Full Circle Fire, specialists in fire detection and alarm systems with more than 30 years’ experience delivering maintenance, upgrades and replacement of obsolete fire detection equipment across NSW.

Important Information

This article provides general information only and is not intended to replace advice based on the specific fire safety systems, approved documentation, building design or regulatory requirements applicable to an individual property.